History of X-ray Crystallography and Early Indian ...iris.physics.iisc.ernet.in/ica/Newsletter/UoH...

Shekhar C. Mande NCCS, Pune

History of X-ray Crystallography and Early Indian Contributions

Talk delivered at the

University of Hyderabad 8-September-2014

Shekhar C. Mande National Centre for Cell Science

Pune


Science


Nature


Discovery of X-rays, 8-Nov-1895

Before March 16, 1945

Recent photograph

X-rays discovered while studying effect of electric current through gas of extremely low pressure Building up on the work of Lenard, Perrin and J J Thomson


Röentgen and possibility of discovering diffraction, 1897

From W. C. Röntgen's Third Communication, March 1897: 'The experiments on the permeability (for X-rays) of plates of constant thickness cut from the same crystal in different orientations, which were mentioned in my first Communication, have been continued. Plates were cut from calcite, quarz, turmaline, beryl, aragonite, apatite and barytes. Again no influence of the orientation on the transparency could be found.

'Ever since I began working on X-rays, I have repeatedly sought to obtain diffraction with these rays; several times, using narrow slits, I observed phenomena which looked very much like diffraction. But in each case a change of experimental conditions, undertaken for testing the correctness of the explanation, failed to confirm it, and in many cases I was able directly to show that the phenomena had arisen in an entirely different way than by diffraction. I have not succeeded to register a single experiment from which I could gain the conviction of the existence of diffraction of X-rays with a certainty which satisfies me.'


Principle of X-ray generation

X-rays are produced when accelerated electrons collide the target Loss of kinetic energy of electrons due to impact is manifested as X-rays Continuous spectrum arises due to deceleration of electrons within the target Characteristic spectrum arises due to inner shell electronic transitions Moseley’s contributions

Kaye, Sommerfield, 1909, “Bremsstrahl” Barkla for characteristic X-rays (called the K- series and the L-series)


1911, An Enigma: Waves of Corpuscles?

WH Bragg interpreted ionization of gases as transfer of energy by photoelectric effect (unaware of Einstein’s work of 1905). X-rays are a stream of particles of neutral charge, or doublets of ± charged. Open arguments with Barkla (upon discovery of polarization of X-rays in 1905) on the wave or corpuscular nature 19 Nov 1908 Nature: As there are few opportunities in Australia for an investigator to place his views quickly before a scientific public, we print the above letter, but with it the correspondence must cease. The subject is more suitable for discussion in special journals devoted to physics than in our columns. Diffraction by a slit: Röentgen, reported unsuccessful attempts, 1897 Sommerfield, fuzziness of fringes due to “diffraction” by a slit caused by considerable spectral range of X-rays.


The first photographs, June 1912

Conceptualized possibly during a walk with PP Ewald, January 1912

http://www.xtal.iqfr.csic.es/Cristalografia/parte_05-en.html


(1) According to Laue, the diffraction in a grating with regularities in three dimensions is most complicated and there is in such a grating a very little chance that a maximum may occur

(2) The deviated spots seem to be much more distinct than should expected when the points were due to diffraction. It is also very difficult to understand how the scattered points can smaller than the middle point due to the primary rays

(3) It is not easily understood how by diffraction a heterogenous beam can give such sharp maxima- and sharp maxima only. If the scattered rays are all due to diffraction, it must be from some homogenous group of rays which are mixed up with the primary one.

Lars Vegard to W. H. Bragg, 26-June, 1912

John Jenkin, William and Lawrence Bragg, Father and Son, The most extraordinary collaboration in Science, Oxford University Press


Bragg’s law

2dsinθ = nλ


Zinc Blende crystals are face centered cubic!


On Pope’s suggestions, Bragg took X-ray photographs of NaCl and reported its structure in June 1913

Structure of NaCl


The properties of the metals must depend, in the first place, on the properties of the individual atoms, and, in the second place, on the atomic arrangement, which is in effect the state of crystallization -William Henry Bragg (1925) “Concerning the Nature of Things”

Potassium 0.89 g/cm3

Diamond 3.52 g/cm3


Allotropes of Carbon: Diamond and Graphite


Nobel Prizes, 1914: Laue, 1915: WH Bragg and WL Bragg, 1916: -, 1917: Charles Barkla

Nobel Prizes of Discovery of X-ray Diffraction


Controversy on Penicillin Structure, 1944 Dorothy Crowfoot Hodgkin

John Cornforth

"If that's the formula of penicillin, I'll give up chemistry and grow mushrooms." Hodgkin was correct, but Cornforth did not become a mushroom farmer.

As she later wrote: "I remember sitting on the steps of the Royal Society ... talking to Bernal and I was telling him that we had solved the structure of penicillin. He said 'you will get the Nobel prize for this.' I said 'I would far rather be elected a Fellow of the Royal Society' and he said 'that's more difficult'."


Polypeptide Chain Configurations in Crystalline Proteins Lawrence Bragg, J. C. Kendrew and M. F. Perutz

Missed the necessity of planar peptide bond unaware of resonance of the peptide group

Bragg to Perutz: I wish I had made you angry earlier !

Pauling’s series of 7 papers in PNAS, 1951


Dimensions of the polypeptide chain.

Pauling L et al. PNAS 1951;37:205-211

©1951 by National Academy of Sciences



Structural Models of Collagen


Madras model of Collagen & Ramachandran Map


“She is trying to get real Laue aufnahmen”


This precedes Huckel’s rules (1931) on separation of sigma and pi orbitals


GN Ramachandran and R Srinivasan, Nature (1961)


Utility of structures in understanding complexity of Nature


Sickle Cell Anemia caused by One Mutation

• Sickle cell anemia is caused by a point mutation in hemoglobin b chain (a is unaffected)

val-his-leu-thr-pro-glu-glu … normal individual

val-his-leu-thr-pro-val-glu … affected individual

• Only one amino acid is change in the entire sequence of the protein

glutamic acid side chain -CH2-CH2-COO– acidic side chain

valine side chain -CH-(CH3)2 nonpolar side chain

• The hemoglobin molecule folds up and

functions (binds oxygen)

• The mutation caused the protein to clump up

in the cells

• The clumping up distorts the cell shape and

makes them architecturally weaker


•The surface of the protein

has side chains sticking

out.

•Polar and charged side

chains help the protein

stay dissolved in water

•The glutamic acid to valine

mutation is a surface

mutation

b

Sickle Cell Anemia caused by One Mutation


Understanding Influenza : A Success Story

Crystal structure of Zanamivir: neuraminidase structure


Future Challenges

• Addressing fundamental problems in biology through understanding structures of many more molecules

• Understanding structure and assembly of large molecular complexes

• Ability to design compounds complementary to defined targets

• Ability to design potential vaccines

• Evolution of molecules that clean up the environment


Thank you!

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